History Lesson

Carcassonne was an important fortified town before the Romans occupied this part of Gaul.
The Romans added to the fortifications. Their distinctive stonework is still clearly visible in many of the inner curtain walls and turrets.
It remained an important military base but was eventually ceded by the Romans to the Visigoths. They in turn lost it to the Frankish invaders, but remained in control of the area just south of Carcassonne. For a while, in the 8th century, Carcassonne was under Islamic authority, until the Franks finally established control over the whole region.
The power of the French king was supplanted in the region by the authority of local families, e.g., the Count of Toulouse, who looked south across the Pyrenees and to Barcelona for support as much as the Franks had done to the North.
The French king, with the support of the Pope, declared a Crusade against the Cathars, which was a heretical Christian sect with many adherents in this part of France. Many say that it was as much because of the desire of the northern nobles to possess the rich lands in this part of France as it was for religious reasons.
In 1209 Carcassonne was besieged during the Albigensian Crusade.
On August 15, Raymond Roger Trencavel, the leader of those in the besieged castle, gave himself up as a hostage so that his people could go free. Instead, the crusaders forced out all the citizens with no possessions but the clothes on their backs.
With flagrant disregard for the laws of chivalry, Trencaval was imprisoned and died within a few months. Unlike at Béziers, however, the Carcassonnais were not slaughtered but forcibly dispersed into the surrounding countryside.
To provide for them, and to rebuild the prosperity of the area, King Louis IX (Saint Louis) authorized in 1247 the building of a new town across the river and away from the walls of the castle. This “bastide” follows a formal ground plan similar to other towns in southern Europe and was surrounded by earthworks and rubble stone walls.
The bridge (Pont Vieux) was built later to connect the new town with the ancient, Iron Age settlement across the river that had become of huge military importance. It was at this time that Carcassonne became once and for all a part of France.
Edward, the Black Prince, sacked the Bastide late in 1355 during his chevauchée from the English region of Gascony to the Mediterranean coast and back. The inhabitants of the ville basse had sought refuge in the fortified town, which he was not able to capture. They offered him a huge sum to spare the lower town, but he refused, and proceeded to fire it and ravage the countryside around. A few stone buildings survived (the churches, for example), but all of the wooden buildings were lost.
Over the following centuries the Bastide was rebuilt following the same plan, but building in stone became standard, even for domestic architecture.
Stone walls and bastions replaced the old fortifications in the years before the French Wars of Religion (late 1500s). During these wars the Bastide was fired upon by the cannon based in the conservative Cité on the hill because it was perceived to be too tolerant.